Asters are a great group of perennials to use in the garden for late-season interest and vibrant colour
A large group of plants, consisting of many different species, each one offering something different in height, colour and design potential; there's an aster for every gardener.
The name of some asters has recently changed, as explained in our "Plantsman: The splitting of Aster," magazine, and they are now known as Symphyotrichum.
Perfect for the back of the border
New England asters, Symphyotrichum novae-angliae, are tall perennials, perfect for the back of the border, reaching 1.2-1.5m (4-5ft) depending on the cultivar. Because of their height they benefit from being staked in spring to ensure they remain upright until the end of the season.
All New England asters are quite upright plants and have very straight stems with narrow, dark-green leaves. The base of taller varieties can become bare, so it is worth underplanting with a lower perennial to hide the bare stem.
During late summer, flower heads form at the tips of the stems and open to produce hundreds of small flowers that cover the plant. They range in colour, depending on the cultivar chosen, but tend to be in shades of pink, purple, mauve and white, all have the same daisy-like structure with a central, yellow disc surrounded by coloured petals or ray florets.
Varieties to look out for
Cultivars to look out for include ‘Harringtons Pink’ which has bright-pink flowers, ‘Rubinschatz’ which has wonderfully rich dark-red flowers and ‘Violetta’ which has dark-purple flowers.
Symphyotrichum are generally easy to grow and like an open, sunny site with well-drained, humus-rich soil. As they are herbaceous the stems need to be cut back to the base in autumn, or spring, and in late spring tall varieties need staking. It is also worth positioning them in a sheltered part of the garden to avoid wind damage.
Symphyotrichum benefit from being divided every four or five years when the older centre part of the plant is removed and the younger growth around the edge of the clump is re-planted. Some Symphyotrichum can suffer with powdery mildew but the New England asters are generally free of mildew and remain healthy through the season.
Asters on display: RHS Garden Hyde Hall
RHS Garden Hyde Hall grows a wide range of asters and Symphyotrichum as they enjoy its open, sunny site and high light levels.
The cultivars mentioned can be found in the island beds and mixed plantings of Hilltop Garden, where they work well with other late flowering perennials such as Anemone x hybrida and Hylotelephium (Herbstfreude Group) ‘Herbstfreude’ both species having large heads of pink flowers. They also work well with grasses such as Calamagrostis brachytricha and Pennisetum alopecuroides, both of which flower in late summer and produce silvery, dark-plumes, making a great late season combination.